Perceiving is difficult for computers- such as perceiving human faces when photo is angled Why is it so difficult to design a perceiving machine? The Stimulus on the Receptors is ambiguous Images cast on your retina are ambiguous (many objects could have created it) – so the perceptual system must determine what is out there that cast this image Inverse projection problem : task of determining the object responsible for an image on retina This involves starting with the retinal image, and extending rays out from the eye Objects can be hidden or blurred People easily perceive the whole object even when only portions of it are visible Use knowledge of the environment to determine what is likely to be present We also can identify blurry objects Objects look different from different viewpoints Humans perceive objects to be the same even when presented with diff angles Viewpoint invariance: ability to recognize an object seen from diff viewpoints Information for human perception Perception is built on the foundation of info from the environment Bottom up processing : light enters eye image on retina electrical signals to brain Starts from the beginning of the system Top down processing: perception involves previous info from environment, expectations, attention Processing originates in the brain Perception is created by a combination of bottom-up and top-down processing Top down processing examples: Perceiving Objects
EX: in blurry images, we perceive objects depending on their orientation & context We perceive based on our knowledge of the kinds of objects likely in diff scenes How meaning influences perception: once we see groupings a certain way, hard to unsee it Hearing words in a sentence Top down influences speech perception Sound signals for speech generally continuous, breaks in sound not always breaks in words Speech segmentation : when knowledge of language lets you hear when 1 word ends & next begins The listener’s experience with language influences perception Experiencing Pain Best example of how top-down processing influences perception Direct pathway model : explained pain in 1950s-1960s Bottom up: Skin receptors (nociceptors) stimulated send signal to brain pain 1960s: some researchers noted situations where additional factors affected pain EX: wounded soldiers denied pain bc the wounds provided an escape from the battlefields Modern research: pain influenced by person’s expectations, attention, distracting stimuli EX: Hospital study: patients were told what to expect & how to relax from pain, requested less painkillers and went home sooner Placebo: a pill that patients believe contains painkillers but doesn’t, actually gives relief 3 • Placebo effect: Key is that patient believes that the substance is an effective therapy, leads the patient to expect a reduction in pain, which occurs Determined by expectation: The perception of pain can increase if attention is focused on the pain or decrease if the pain is ignored or attention
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